A city in Texas won't give people hurricane aid unless they promise not to boycott Israel
American Civil Liberties Union says application form for flooding relief grants 'reminiscent of McCarthy-era loyalty oaths'
How the heck are they going to enforce that? Follow folks to the supermarket and force them to buy Isreali products?
I would imagine its more of a speech thing. If you just silently boycott they likely wont know or be able to prove it, but if you publicly say that you are boycotting Israel (which is something that makes such efforts more effective anyway since boycotts are a group action), or perhaps advocate for it in a way that makes it seem likely that you are doing it yourself, then they might be able to go after you for that (or at least the fear that they could so so, even if they never actually bother, might deter some people).
The tail wagging the dog